I have the same error here on localhost.
The error in console is:
500 when post http://localhost:8008/wp-test/wp-admin/admin-ajax.php

I opened the request tab and download the “parallax” demo from https://kriesi.at/themes/demo-downloads/download/417/
and paste it on D:/xampp/htdocs/wp-test/wp-content/uploads/dynamic_avia/avia_demo_files/parallax/
but how can I manually install it?